Reddit mentions of Materials Selection in Mechanical Design, Third Edition

This is called 'materials selection' and Ashby is the main pioneer (e.g. https://www.amazon.co.uk/Materials-Selection-Mechanical-Design-Michael/dp/0750661682 ). Otherwise, I'd say be aware for each alloy or class of alloys

• Cost, and how it varies with alloying additions like Ni in steels
  
• Stiffness, which doesn't change that much
  
• Yield strength, and how it varies with temperature and prior heat treatment
  
• Toughness, and how to improve it with and without sacrificing yield strength
  
• Corrosion resistance, and the particular kinds (oxidation, chloride, hydrogen) and why these are industrially relevant
  
• Fatigue and creep
  
• Formability issues, such as weldability and machinability

Some comparative info, I can't write a lecture today at work, maybe later.

General curve information Plastic region does not mean "made of plastic" deformation before in the elastic region is recoverable, deformation in the plastic region is not recoverable.

Common Plastics

Pure Aluminum

Note that Al alloys and heat treatments can greatly vary this shape, but the idea is to have a comparitive order of manitude when compared to the plastic for the tensile stress.

It's also important to know that the stress is proportional to the cross sectional area. meaning, roughly, that the 10 order of magnitude difference in yield stress between Al and plastics means that a plastic with 10 times the thickness of Al would resist the same applied force in tension.

In other words, Apple Al phones are made of super thin Al, and the phones are super thin. To make them out of plastic would mean the frame would have to be 10 x thicker to have the same deformation resistance, or larger to have better resistance.

There are other major things at play here, like structural rigidity due to geometry, alloying, heat treatment, applied loads etc, but I'm trying to give a gross simplification.

Food for thought: Note that Titanium is not orders of magnitude sronger than Al, but Al is desirable often due to cost and strength to weight ratio...

edit: Recommended further reading on material selection and design. Appendix of this book is amazing.